It was the internet story of 2007, the website that brought you sneezing pandas, laughing babies, an epic battle on the African savannah and a guest appearance by Tony Blair in a video starring George Bush's dog.

But for any web surfers in China, these and other gems purveyed by the video-sharing phenomenon YouTube look likely to become impossible to access, after the authorities signalled yesterday that they would no longer tolerate the "broadcast of degenerate thinking" on the internet.

In a move apparently aimed at YouTube and scores of other smaller rivals, the Chinese authorities announced that all video-sharing websites must have official government approval before they can be accessed by Chinese surfers. New rules governing online content announced by the state administration of radio, film and television also stipulate that from the end of January only state-owned or controlled companies would be given licences to upload video in China.

"Those who provide internet video services should insist on serving the people ... and abide by the moral code of socialism," say the new guidelines. Licensed companies would be responsible for upholding national security, maintaining a "healthy online environment" and would be required to ban any videos that damage the country's reputation.

The upshot could be severe for China's 150 million internet users, who can now expect content to be dominated by footage that helps "promote overall social progress and harmony" and a "socialist morality"; think party congresses, military march-pasts and gymnastic medal hopes for the 2008 Beijing Olympics.

China, which now has the second largest number of internet users behind the United States, already enforces severe restrictions on web content, using its so-called "great firewall" to block websites and information deemed controversial.

The regime has a small army of up to 30,000 internet "monitors" who police the online community in China, rapidly erasing critical comment from chatrooms and bulletin boards or patrolling internet bars watching for console sleight of hand.

The crackdown is the product of Chinese government concern about the rapid growth in Web 2.0 sites, which allow the country's technically savvy youth to distribute homemade videos, photos and opinions to the rest of the world over the internet.

But even though Beijing severely restricts Chinese media outlets, it has been reluctant to strike too hard against dotcoms because of their growing economic importance. Online video has exploded in popularity inside China in recent years, and the country now boasts more than 500 websites that allow people to put their own video on to the internet.

The new rules are similar to those that China already enforces on online news providers, where only a select number of licensed companies can create their own content in addition to the officially sanctioned state news channels. Rules have also been drawn up which target the elimination of subversive content and promote "civilised" news and information.

As well as a series of crackdowns against "cyber-dissidents" accused of spreading politically sensitive information abroad, the government has insisted that local bloggers register under their real names through officially approved sites. Those sites, including sina.com, are obliged to monitor and delete politically sensitive content themselves.

However, with western companies keen to sell to China's formidable online populace, the government has sought to bring in foreign investment by offering permission to set up lucrative Chinese operations only on the condition that they yield to the country's strict censorship rules.

A YouTube spokesperson said the new regulations "could be a cause for concern, depending on the interpretation".

"We believe that the Chinese government fully recognises the enormous value of online video and will not enforce the regulations in a way that could deprive the Chinese people of its benefits and potential for business and economic development, education and culture, communication and entertainment."